Indexzugriff

Indexzugriff, also known as indexed access or index lookup, refers to the process of retrieving data from a database table by using an index. An index is a data structure, typically a B-tree or hash table, that stores a subset of a table's columns in a sorted order. This sorted order allows the database system to quickly locate specific rows without having to scan the entire table.

When a query involves a condition on an indexed column, the database can consult the index instead of performing a full table scan. The index provides direct pointers to the relevant data blocks, significantly reducing the amount of data that needs to be read from disk. This speeds up query execution, especially for large tables and queries that filter or sort data based on indexed columns.

The effectiveness of indexzugriff depends on several factors. The presence of a suitable index is paramount. The type of index (e.g., B-tree, hash) and the columns included in the index also play a crucial role. Query design is also important; queries that can effectively utilize the index, such as those with equality conditions or range queries on indexed columns, benefit the most. Conversely, queries that cannot leverage an index will resort to full table scans, which can be much slower. Index maintenance, including creation, updating, and deletion, incurs overhead, and the database optimizer makes decisions about whether to use an index based on estimated query costs.